The γ-ketoacetal compounds of general formula (A) shown below are known as intermediates for producing a 4-methyl-1,2-diarylpyrrole derivative (Japanese Patent Publication (Kokai) Number 2000-80078) which is known as a useful analgesic (see U.S. Pat. No. 5,908,858)
(wherein Ar1 represents an aryl group which may be optionally substituted with a substituent(s), R1 and R2 each independently represent a lower alkyl group or R1 and R2 taken together represent a trimethylene group or the like). The process for producing said γ-ketoacetal compounds, wherein nitromethane (CH3NO2) and a base are used, is documented (Japanese Patent Publication (Kokai) Number 2000-80078). Since nitromethane is apt to explode, the process must be carefully carried out. There are hence some considerable problems in the process; for example, the process for preparation of γ-ketoacetal compounds, especially in a large-scale production, becomes particularly complex in order to avoid explosions occurring.